Polymeric films can be found in a variety of different applications such as food packaging, stretch wrap, plastic bags, and the like. Biaxially oriented film extrusion is a common technique for preparing polymeric films.
Biaxially oriented film is normally prepared by extruding a molten resin through a round die. The resin is forced around a mandrel inside the die, shaped into a sleeve, and extruded through an opening in the round die in the form of a tube. The molten tube is normally formed around an air pressure cylinder or chilled water caliper as it exits the die. The tube may be solidified by passing through a cooling ring. The tube then passes through a nip roll that collapses the tube into a relatively flat tube, also referred to as the “tape.” Process gases can frequently be trapped within the tape. The tape can then be driven forward over a series of idler rolls and into an electronic crosslinking unit (ECLU). At the ECLU the tape is exposed to an irradiation source that promotes crosslinking.
The irradiating process typically produces hydrogen gas that is trapped within the tape. Hydrogen gas trapped within the tape can be problematic for several reasons. The gas sometimes causes small ignitions that damage the tape and that can result in temporary line stoppages. Hydrogen gas removal requires additional equipment on the production line to facilitate its removal. For example, slits can be created in the tape to help prevent the accumulation of hydrogen gas by providing openings through which the gas can escape. A heat seal is normally used to close the slits after most of the gases have escaped from within the tape. Forming slits and heat seals is an undesirable solution because this action can result in additional downtime. As a result, the entire process is less efficient, more complex, and can require a production line having a larger footprint.